#
# Copyright 2009 Facebook
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
#
#  Based heavily on the tornado web server ioloop.py


"""An I/O event loop for ZeroMQ non-blocking sockets.
This is based off of the Tornado web server IOLoop. This is not intended
to be thread safe. One IOLoop per process.

Typical applications will use a single `IOLoop` object, in the
`IOLoop.instance` singleton.  The `IOLoop.start` method should usually
be called at the end of the ``main()`` function.  Atypical applications may
use more than one `IOLoop`, such as one `IOLoop` per thread, or per `unittest`
case.

In addition to I/O events, the `IOLoop` can also schedule time-based events.
`IOLoop.add_timeout` is a non-blocking alternative to `time.sleep`.
"""

from __future__ import with_statement

import datetime
import heapq
import os
import sys
import errno
import logging

import time
import traceback

import zmq
from zmq.utils.strtypes import asbytes

try:
    import signal
except ImportError:
    signal = None

try:
    import fcntl
except ImportError:
    if os.name == 'nt':
        from zmq.eventloop import win32_support
        fcntl = win32_support
    else:
        raise

from zmq import (
        Poller,
        POLLIN, POLLOUT, POLLERR,
        ZMQError, ETERM
        )


class IOLoop(object):
    """A ZeroMQ polling I/O loop.

    We use epoll (Linux) or kqueue (BSD and Mac OS X; requires python
    2.6+) if they are available, or else we fall back on select(). If
    you are implementing a system that needs to handle thousands of
    simultaneous connections, you should use a system that supports either
    epoll or queue.

    Example usage for a simple TCP server::

        import errno
        import functools
        import ioloop
        import socket

        def connection_ready(sock, node, events):
            while True:
                try:
                    connection, address = sock.accept()
                except socket.error, e:
                    if e.args[0] not in (errno.EWOULDBLOCK, errno.EAGAIN):
                        raise
                    return
                connection.setblocking(0)
                handle_connection(connection, address)

        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        sock.setblocking(0)
        sock.bind(("", port))
        sock.listen(128)

        io_loop = ioloop.IOLoop.instance()
        callback = functools.partial(connection_ready, sock)
        io_loop.add_node(node, callback, io_loop.READ)
        io_loop.start()

    """
    # Use the zmq events masks
    NONE = 0
    READ = POLLIN
    WRITE = POLLOUT
    ERROR = POLLERR

    def __init__(self, impl=None):
        self.zpoller = Poller()
        self._nodes = {}
        self._events = {}
        self._callbacks = []
        self._timeouts = []
        self._running = False
        self._stopped = False
        self._blocking_signal_threshold = None

        # Create a pipe that we send bogus data to when we want to wake
        # the I/O loop when it is idle
        #if os.name != 'nt':
        #    r, w = os.pipe()
        #    self._set_nonblocking(r)
        #    self._set_nonblocking(w)
        #    self._set_close_exec(r)
        #    self._set_close_exec(w)
        #    self._waker_reader = os.fdopen(r, "rb", 0)
        #    self._waker_writer = os.fdopen(w, "wb", 0)
        #else:
        #    self._waker_reader = self._waker_writer = win32_support.Pipe()
        #    r = self._waker_writer.reader_fd
        #self.add_handler(r, self._read_waker, self.READ)

    @classmethod
    def instance(cls):
        """Returns a global IOLoop instance.

        Most single-threaded applications have a single, global IOLoop.
        Use this method instead of passing around IOLoop instances
        throughout your code.

        A common pattern for classes that depend on IOLoops is to use
        a default argument to enable programs with multiple IOLoops
        but not require the argument for simpler applications::

            class MyClass(object):
                def __init__(self, io_loop=None):
                    self.io_loop = io_loop or IOLoop.instance()
        """
        if not hasattr(IOLoop, "_instance"):
            IOLoop._instance = IOLoop()
        return IOLoop._instance

    @staticmethod
    def initialized():
        """Returns true if the singleton instance has been created."""
        return hasattr(IOLoop, "_instance")

    def install(self):
        """Installs this IOloop object as the singleton instance.

        This is normally not necessary as `instance()` will create
        an IOLoop on demand, but you may want to call `install` to use
        a custom subclass of IOLoop.
        """
        assert not IOLoop.initialized()
        IOLoop._instance = self

    def close(self, all_sockets=False):
        """Closes the IOLoop, freeing any resources used.

        If ``all_sockets`` is true, all file descriptors registered on the
        IOLoop will be closed (not just the ones created by the IOLoop itself.
        """
        if all_sockets:
            for node, handler in self._nodes.items()[:]:
                try:
                    node.close()
                except Exception:
                    logging.debug("error closing socket:node %s:%s",
                                (socket, node), exc_info=True)

    def add_node(self, node, events):
        """Registers the given handler to receive the given events for node."""
        logging.debug("IOLoop.add_node(node:%s, events:%X)" % (node, events))
        self._nodes[node.socket] = node
        self.zpoller.register(node.socket, events | self.ERROR)

    def update_node(self, node, events):
        """Changes the events we listen for node."""
        logging.debug("IOLoop.update_node(node:%s, events:%2.2X)" %
                    (node, events))
        self.zpoller.modify(node.socket, events | self.ERROR)

    def remove_node(self, node):
        """Stop listening for events on node."""
        logging.debug("IOLoop.remove_node(node:%s)" % (node))
        self._nodes.pop(node.socket, None)
        self._events.pop(node.socket, None)
        try:
            self.zpoller.unregister(node.socket)
        except (OSError, IOError):
            logging.debug("Error deleting node from IOLoop", exc_info=True)

    def set_blocking_signal_threshold(self, seconds, action):
        """Sends a signal if the ioloop is blocked for more than s seconds.

        Pass seconds=None to disable.  Requires python 2.6 on a unixy
        platform.

        The action parameter is a python signal handler.  Read the
        documentation for the python 'signal' module for more information.
        If action is None, the process will be killed if it is blocked for
        too long.
        """
        if not hasattr(signal, "setitimer"):
            logging.error(("set_blocking_signal_threshold "
                "requires a signal module "
                 "with the setitimer method"))
            return
        self._blocking_signal_threshold = seconds
        if seconds is not None:
            signal.signal(signal.SIGALRM,
                 action if action is not None else signal.SIG_DFL)

    def set_blocking_log_threshold(self, seconds):
        """Logs a stack trace if the ioloop is blocked for more than s seconds.
        Equivalent to set_blocking_signal_threshold(seconds, self.log_stack)
        """
        self.set_blocking_signal_threshold(seconds, self.log_stack)

    def log_stack(self, signal, frame):
        """Signal handler to log the stack trace of the current thread.

        For use with set_blocking_signal_threshold.
        """
        logging.warning('IOLoop blocked for %f seconds in\n%s',
                  self._blocking_signal_threshold,
                  ''.join(traceback.format_stack(frame)))

    def start(self):
        """ Starts the I/O loop.
        The loop will run until one of the I/O handlers calls stop(), which
        will make the loop stop after the current event iteration completes.
        """

        if logging.getLogger().getEffectiveLevel() == logging.DEBUG:
            logging.debug("IOLoop.start() len(nodes) : %s" %
                        (len(self._nodes),))
            for socket, node in self._nodes.items():
                logging.debug("IOLoop.start() node : %s" % (node,))

        if self._stopped:
            self._stopped = False
            return

        self._running = True
        while True:
            # Never use an infinite timeout here
            # In pyzmq, we need to multiply the timeout by 1000 because
            # the poll interface in pyzmq that is used here takes the timeout
            # in ms. The value of 0.2 that exists in tornado is in seconds.
            poll_timeout = 0.2 * 1000

            # Prevent IO event starvation by delaying new callbacks
            # to the next iteration of the event loop.
            callbacks = self._callbacks
            self._callbacks = []
            for callback in callbacks:
                self._run_callback(callback)

            if self._timeouts:
                now = time.time()
                while self._timeouts:
                    if self._timeouts[0].callback is None:
                        # the timeout was cancelled
                        heapq.heappop(self._timeouts)
                    elif self._timeouts[0].deadline <= now:
                        timeout = heapq.heappop(self._timeouts)
                        self._run_callback(timeout.callback)
                    else:
                        milliseconds = self._timeouts[0].deadline - now
                        poll_timeout = min(milliseconds, poll_timeout)
                        break

            if self._callbacks:
                # If any callbacks or timeouts called add_callback,
                # we don't want to wait in poll() before we run them.
                poll_timeout = 0.0

            if not self._running:
                break

            if self._blocking_signal_threshold is not None:
                # clear alarm so it doesn't fire while poll is waiting for
                # events.
                signal.setitimer(signal.ITIMER_REAL, 0, 0)

            try:
                sockets = self.zpoller.poll(timeout=poll_timeout)
            except ZMQError:
                e = sys.exc_info()[1]
                if e.errno == ETERM:
                    # This happens when the zmq Context is closed;
                    # we should just exit.
                    self._running = False
                    self._stopped = True
                    break
                else:
                    raise
            except Exception:
                e = sys.exc_info()[1]
                # Depending on python version and IOLoop implementation,
                # different exception types may be thrown and there are
                # two ways EINTR might be signaled:
                # * e.errno == errno.EINTR
                # * e.args is like (errno.EINTR, 'Interrupted system call')
                if (getattr(e, 'errno', None) == errno.EINTR or
                    (isinstance(getattr(e, 'args', None), tuple) and
                    len(e.args) == 2 and e.args[0] == errno.EINTR)):
                    logging.warning("Interrupted system call", exc_info=1)
                    continue
                else:
                    raise

            if self._blocking_signal_threshold is not None:
                signal.setitimer(signal.ITIMER_REAL,
                     self._blocking_signal_threshold, 0)

                # Pop one node at a time from the set of pending nodes and run
            # its handler. Since that handler may perform actions on
            # other file descriptors, there may be reentrant calls to
            # this IOLoop that update self._events
            self._events.update(sockets)
            while self._events:
                socket, events = self._events.popitem()
                try:
                    logging.debug(("IOLoop.start(socket:%s, events:%X)"
                                " calling poll_handler") %
                               (socket, events))
                    self._nodes[socket].poll_handler(events)
                except (OSError, IOError), e:
                    if e.args[0] == errno.ETERM:
                        # Happens when the client closes its socket
                        pass
                    else:
                        logging.error("Exception in I/O handler for socket %d",
                                socket, exc_info=True)
                except Exception:
                    logging.error("Exception in I/O handler for socket %s",
                            socket, exc_info=True)
        # reset the stopped flag so another start/stop pair can be issued
        self._stopped = False
        if self._blocking_signal_threshold is not None:
            signal.setitimer(signal.ITIMER_REAL, 0, 0)

    def stop(self):
        """Stop the loop after the current event loop iteration is complete.
        If the event loop is not currently running, the next call to start()
        will return immediately.

        To use asynchronous methods from otherwise-synchronous code (such as
        unit tests), you can start and stop the event loop like this::
          ioloop = IOLoop()
          async_method(ioloop=ioloop, callback=ioloop.stop)
          ioloop.start()
        ioloop.start() will return after async_method has run its callback,
        whether that callback was invoked before or after ioloop.start.
        """
        logging.debug("IOLoop.stop()")
        self._running = False
        self._stopped = True
        #self._wake()

    def running(self):
        """Returns true if this IOLoop is currently running."""
        return self._running

    def add_timeout(self, deadline, callback):
        """Calls the given callback at the time deadline from the I/O loop.

        Returns a handle that may be passed to remove_timeout to cancel.

        ``deadline`` may be a number denoting a unix timestamp (as returned
        by ``time.time()`` or a ``datetime.timedelta`` object for a deadline
        relative to the current time.
        """
        timeout = _Timeout(deadline, callback)
        heapq.heappush(self._timeouts, timeout)
        return timeout

    def remove_timeout(self, timeout):
        """Cancels a pending timeout.

        The argument is a handle as returned by add_timeout.
        """
        # Removing from a heap is complicated, so just leave the defunct
        # timeout object in the queue (see discussion in
        # http://docs.python.org/library/heapq.html).
        # If this turns out to be a problem, we could add a garbage
        # collection pass whenever there are too many dead timeouts.
        timeout.callback = None

    def add_callback(self, callback):
        """Calls the given callback on the next I/O loop iteration.

        It is not considered safe to call this method from another thread.
        """
        list_empty = not self._callbacks
        self._callbacks.append(callback)
        #self._wake()
    #def _wake(self):
    #    try:
    #        self._waker_writer.write(asbytes("x"))
    #    except IOError:
    #        pass

    def _run_callback(self, callback):
        try:
            callback()
        except Exception:
            self.handle_callback_exception(callback)

    def handle_callback_exception(self, callback):
        """This method is called whenever a callback run by the IOLoop
        throws an exception.

        By default simply logs the exception as an error.  Subclasses
        may override this method to customize reporting of exceptions.

        The exception itself is not passed explicitly, but is available
        in sys.exc_info.
        """
        logging.error("Exception in callback %r", callback, exc_info=True)

    #def _read_waker(self, fd, events):
    #    s=None
    #    try:
    #        while True and s is None:
    #            s = self._waker_reader.read()
    #    except IOError:
    #        pass

    #def _set_nonblocking(self, fd):
    #    flags = fcntl.fcntl(fd, fcntl.F_GETFL)
    #    fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)

    #def _set_close_exec(self, fd):
    #    flags = fcntl.fcntl(fd, fcntl.F_GETFD)
    #    fcntl.fcntl(fd, fcntl.F_SETFD, flags | fcntl.FD_CLOEXEC)


class _Timeout(object):
    """An IOLoop timeout, a UNIX timestamp and a callback"""

    # Reduce memory overhead when there are lots of pending callbacks
    __slots__ = ['deadline', 'callback']

    def __init__(self, deadline, callback):
        if isinstance(deadline, (int, long, float)):
            self.deadline = deadline
        elif isinstance(deadline, datetime.timedelta):
            self.deadline = (
                    time.time() + _Timeout.timedelta_to_seconds(deadline))
        else:
            raise TypeError("Unsupported deadline %r" % deadline)
        self.callback = callback

    @staticmethod
    def timedelta_to_seconds(td):
        """Equivalent to td.total_seconds() (introduced in python 2.7)."""
        return (td.microseconds + (
                td.seconds + td.days * 24 * 3600) * 10 ** 6) / float(10 ** 6)

    # Comparison methods to sort by deadline, with object id as a tiebreaker
    # to guarantee a consistent ordering.  The heapq module uses __le__
    # in python2.5, and __lt__ in 2.6+ (sort() and most other comparisons
    # use __lt__).
    def __lt__(self, other):
        return ((self.deadline, id(self)) <
            (other.deadline, id(other)))

    def __le__(self, other):
        return ((self.deadline, id(self)) <=
                (other.deadline, id(other)))


class PeriodicCallback(object):
    """Schedules the given callback to be called periodically.

    The callback is called every callback_time milliseconds.

    `start` must be called after the PeriodicCallback is created.
    """
    def __init__(self, callback, callback_time, io_loop=None):
        self.callback = callback
        self.callback_time = callback_time
        self.io_loop = io_loop or IOLoop.instance()
        self._running = False

    def start(self):
        """Starts the timer."""
        self._running = True
        self._next_timeout = time.time()
        self._schedule_next()

    def stop(self):
        """Stops the timer."""
        self._running = False

    def _run(self):
        if not self._running:
            return
        try:
            self.callback()
        except Exception:
            logging.error("Error in periodic callback", exc_info=True)
        self._schedule_next()

    def _schedule_next(self):
        if self._running:
            current_time = time.time()
            while self._next_timeout <= current_time:
                self._next_timeout += self.callback_time / 1000.0
            self.io_loop.add_timeout(self._next_timeout, self._run)

#PeriodicCallback
